The invention relates to a driveshaft comprising three components, i.e., a first attaching element, a second attaching element and a tube element arranged therebetween. Furthermore, the invention relates to a method of producing such a driveshaft.
When producing driveshafts, especially those used in propeller shafts for drives in motor vehicles, the attaching elements are provided with seat faces which, in a centered way, are received in the tube bore of the tube element. The connection between the tube element and the attaching element is effected welding. Furthermore, it is known to provide each of the attaching elements with a cylindrical projection whose diameter is substantially adapted to the tube diameter, and to connect the tube element to the attaching elements by friction welding. In the case of both design solutions, the offset results in out-of-balance at the finish-produced driveshafts. This is also the case if the connection is effected by magnetic arc welding, because both welding technologies, i.e. friction welding and magnetic arc welding, require axial pressure for producing the connection. Under such pressure, the tube element at the attaching element slides out of the central position in the radial direction and, in the connected condition it is usually positioned eccentrically. In particular, this applies to thin-walled tubes.
In the case of connections where there is provided a centering seat and where, in the region of the seat face at the attaching element, there is provided a V-weld formed by an end face of the tube element and a shoulder of the attaching element, with the positioning of the tube element and the attaching element in the axial direction being predetermined in a defined way, there occur considerable deviations in length if the tube elements are not accurately produced to a specific length. This means that it is necessary to develop complicated and expensive methods for machining the tubes. In addition, it is necessary to take into account the axial run-out which, even if its value is acceptable from a production-technical point of view, leads to an inclined position of the attaching elements in the tube element, which is not permissible.
It is therefore an object of the invention to propose a driveshaft and a method of producing a driveshaft, for which purpose there is required a simple, cost-effective production process which permits an accurate connection even of thin-walled tubes comprising good concentric running characteristics and small length tolerances.
In accordance with the invention, the foregoing and other objects are achieved by providing a driveshaft comprising three components each having an individual longitudinal axis: a first attaching element, a second attaching element, and a straight tube element which is arranged therebetween. The straight tube element has a first end face and a second end face and a tube bore. The two attaching elements each comprise a cylindrical receiving face, which cylindrical receiving faces, starting from the two end faces, are arranged at least along part of their axial length in the tube bore. Furthermore, the tube bore has a greater diameter than the receiving faces. The individual components, by means of their individual longitudinal axes, are aligned radially, independently of one another, on a longitudinal reference axis and connected by welds which are located between the end faces of the tube element and the associated receiving faces. The first end face of the tube element, which first end face faces the first attaching element, is arranged at a predetermined distance from a first reference face or a first reference axis of the first attaching element. The total nominal length is determined by the distance between the first reference face or the first reference axis and a second reference face or a second reference axis of the second attaching element.
Furthermore, said objective is achieved by providing a method of producing a driveshaft from a first attaching element, a second attaching element and a tube element which each comprise an individual longitudinal axis and which are connected to one another by welds. The attaching elements each comprise a cylindrical receiving face and the tube element comprises a cylindrical tube bore as well as a first end face and a second end face. The receiving faces are produced with a diameter which, relative to the diameter of the tube bore, permits a predetermined maximum radial relative adjustment. Furthermore, the first attaching element, the second attaching element and the tube element, by means of their individual longitudinal axes, are axially aligned to one another and are radially aligned on a longitudinal reference axis and thereafter connected by producing a weld between the first receiving face and the first end face and between the second receiving face and the second end face.
The two solutions in accordance with the invention achieve a driveshaft with minimized out-of-balance characteristics. The present driveshaft, even at high speeds, features quiet running characteristics and can be produced with small construction tolerances. As compared to the tube bore of the tube element, the diameter of the receiving faces of the attaching elements is smaller such that, in cases of limited tolerances, there is not yet any line contact between the receiving face and the tube bore, thus permitting a radial displacement of the parts relative to one another until the individual longitudinal axes of the parts are concentrically aligned on the longitudinal reference axis. It is possible to achieve a driveshaft with reduced out-of-balance because the reference axis is determined by the receiving points of a device for the attaching elements and the tube element.
A further advantage of the present invention is that any construction tolerances of the individual components affecting the total nominal length do not exert any special influence. In particular, it is possible to produce the lengths of tube by simple production methods such as sawing or cutting. Tolerances regarding the overall length are compensated for by introducing the second attaching face of the second attaching element into the tube bore more or less deeply. As the weld is produced between the respective end face of the tube element and the associated attaching face of one of the attaching elements, any length tolerances or any axial run-out do not adversely affect the connection or the dimensional accuracy of the driveshaft in the radial or axial direction. The axial alignment of the individual longitudinal axes of the components can take place simultaneously with, or after, the radial alignment of the components by means of their individual longitudinal axes relative to the longitudinal reference axis, but such alignment has to take place prior to the welding operation.
The welds are preferably produced by plasma welding. Such a welding method is particularly suitable for bridging larger gap widths. Furthermore, it is possible, first, to carry out only one alignment and fixing operation of the first attaching element relative to the tube element, i.e. the radial alignment relative to a longitudinal reference axis. The first end face of the tube element is thus axially aligned, which first end face faces the attaching element, relative to a predetermined distance from a first reference face or reference axis of the first attaching element. The two parts can then be connected to one another by a weld. Subsequently, the second attaching element is radially aligned relative to the tube element by using the longitudinal reference axis and additionally effecting an axial setting to the total nominal length by effecting an alignment to the predetermined second distance between the first reference face or first reference axis and a second reference face or second reference axis of the second attaching element. The parts are subsequently connected to one another by a weld.
However, in a preferred embodiment, the connection and alignment of both end faces of both attaching elements are effected simultaneously. This also applies to producing the two welds. To accelerate the process, it is also possible to produce the two welds between the end faces and the associated attaching faces by circumferentially distributed welding guns. The welds for connecting the first receiving face to the first end face and the second receiving face to the second end face can be produced simultaneously. It is advantageous to use a more advanced plasma welding method which is characterized by a reliable welding start, a higher welding speed and reduced distortion. There occurs no spatter, so that there is no need for any subsequent treatment. Such a method is known, for example, under the name of xe2x80x9cPlasma Braze Processxe2x80x9d developed by ARC KINETICS (38 The Fairway, Daventry, Northants, NN11 4NW, England).
Other objects and advantages will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.